Recently, from the standpoint of global environmentalism, there is a positive trend in industrial painting toward the use of aqueous paint in place of solvent type paint to reduce discharges of organic solvents. Aqueous paint is a conducting paint which is low in electrical resistance, so that an aqueous paint coating apparatus should be constructed in such a way as to prevent leakage of high voltage currents toward a paint supply source on the grounded side through a paint supply passage. As a measure for preventing leaks of high voltage currents (as a voltage block means), it has been known in the art to provide a plural number of external electrodes on the outer peripheral side of a rotary atomizing head, thereby discharging a high voltage to indirectly electrify paint particles which are sprayed forward from the rotary atomizing head (see, for example, Patent Literature 1: Japanese Patent Laid-Open No. H4-215864, Patent Literature 2: Japanese Laid-Open No. H6-7709, and Patent Literature 3: U.S. Pat. No. 6,896,735).
In Patent Literature 1 mentioned above, a shielding projection of insulating material is provided on the front side of each external electrode in the proximity of a rotary atomizing head to prevent short-circuiting of a high voltage between an external electrode and rotary atomizing head. This arrangement is effective for preventing short-circuiting between an external electrode and rotary atomizing head by existence of the shield projection. However, due to the existence of shielding projections as obstacles in the way of sprayed paint particles, there is a tendency that an ionizing zone which imparts electric charges to paint particles is formed at a remote position from the rotary atomizing head so that it is difficult to electrify sprayed paint particles to a sufficient degree.
Further, disclosed in Patent Literature 2 is an electrostatic coating apparatus which is equipped with a plural number of external electrodes in a ring-like formation on the outer peripheral side of a rotary atomizing head thereby to impart electric charges to paint particles, along with an annular auxiliary electrode which is disposed to circumvent the outer peripheral side of a plural number of the external electrodes. In this case, as compared with the external electrodes, a higher voltage is applied to the auxiliary electrode thereby to enhance the strength of an electric field between the auxiliary electrode and a coating object for prevention of backward drifting of paint particles. However, since the external electrodes are located in the proximity of a rotary atomizing head, there are tendencies toward frequent short-circuiting between an external electrode and the rotary atomizing head. In order to prevent short-circuiting between an external electrode and the rotary atomizing head, it becomes necessary to apply a lower voltage to the external electrodes despite a difficulty of charging paint particles to a satisfactory degree.
Further, disclosed in Patent Literature 3 above are a plural number of external electrodes which are fitted in a housing of a coating apparatus in a ring-like formation. In this case, fore ends of the external electrodes are located in close proximity of the housing, so that electrification of the housing takes place only in the ambience of fore distal ends of the external electrodes when a high voltage is discharged from fore distal ends of the external electrodes. Thus, this coating apparatus has a problem that charged paint particles on the float tend to deposit on the housing.